The present invention relates to metal cutting, and more particularly, to a boring tool for performing both the rough and finish cutting operations.
In the production of metal parts having a bore, it is often necessary to perform a rough boring operation to remove a substantial thickness of metal, followed by a finish cutting operation removing a small thickness of metal to maximize the smoothness of the surface. It is general practice in the machining art to perform the rough cut on the work piece with one tool, and then use a different tool for the finish cutting operation. In doing this, it is then at least necessary to carry out these separate steps: (1) perform the rough cut; (2) retract the rough cut tool as the boring bar reverses its direction and moves back through the bore that has been formed; (3) remove the tool and reset the machine; (4) perform the finish cut; and (5) retract and reverse feed the finish cut tool. The entire operation is time-consuming and inefficient.
In an attempt to make the operation more efficient, some machine shops prefer to have one machine perform the rough cut and a second machine perform the finish cut. However, as will be recognized, this still falls far short of an operation that is efficient in terms of motion and time.
There have been attempts to provide a boring bar to provide both the rough cut and the finish cut operation. These previous attempts may be exemplified by the U.S. Pat. to Briney, et al., No. 3,233,480, issued Feb. 8, 1966. In this prior patent, the boring bar utilizes a complicated set of centrifugal clutches and actuating mechanisms to provide two cutting depths. A separate actuator mechanism is required to shift the single cutter radially outwardly in order to provide the finish cut. The shifting is controlled by a plurality of concentric rotatable discs and it has been found in practice that the shifting movement is unstable and inaccurate so that the finish cut leaves much to be desired. Furthermore, because a separate actuation is required, the speed of the boring bar is limited, and in fact relatively time-consuming.
In another type of tool that has been proposed, a boring tool is provided having dual cutters and a retractable tool to deburr the entrance and exit to the bored hole. The retractable tool does not perform any cutting function on the inside of the work piece and thus is not capable of performing both the rough and the finished boring operations. This type of tool is shown by the Busch U.S. Pat. No. 2,878,696, issued May 24, 1959.
Contrary to the previous attempts in this art, I have recognized a need for a dual cut boring tool assembly that is simple in design and requires no special operation during the machining cycle in order to activate or deactivate the cutting tools. I have set out to provide a tool assembly that will inherently perform both the rough cut and the finish cut simply by positioning the tools in the proper cutting relationship at the proper time during the cycle.